The present invention relates to converting a digital signal to an analog signal.
Digital to analog conversion is widely applied in electronic signal processing. Known conversion techniques use so-called current steering Nyquist digital to analog converters (DAC) summing binary weighted current sources to form the analog signal. Such Nyquist DACs offer high-speed conversion with relatively few current sources. The output analog signal shows inaccuracy due to mismatch of the weighted current sources, in particular with large current range. To minimize such mismatch requires a difficult layout. Furthermore a hardware filter is necessary, e.g. a low pass filter, for filtering the output signal to suppress harmonic content in the output signal.
Another known conversion technique uses a so-called multi-bit Delta-Sigma converter summing only equal current sources and thus offering high accuracy at reduced conversion speed due to over-sampling. A subset of n out of in total N equal current sources can be selected using a dynamic element matching (DEM) unit by randomly selecting a subset of equal current sources to further improve accuracy by averaging out mismatch errors of the individual equal current sources. The mismatch error is converted into noise. A hardware filter is still necessary for filtering the output signal.
Another known conversion technique uses so-called segmented NYQUIST DAC wherein a number of M most significant bits (MSB) are processed to 2M equal current sources and a number of L least significant bits (LSB) are processed to L binary weighted current sources. In an output stage the outputs of the 2M equal current sources and the L binary weighted sources are summed. Such segmented NYQUIST DACs offer a reduction of the current range of the weighted current sources used for the LSB. For the MSB a subset of equal current sources can be selected using a dynamic element matching (DEM) unit by randomly selecting a subset of equal current sources to further improve accuracy by averaging out mismatch errors of the individual equal current sources. The mismatch error is converted into noise. A hardware filter is still necessary for filtering the output signal.